Phosphatidylinositol is one of a number of phospholipids found in cell membranes which play an important role in intracellular signal transduction. Cell signaling via 3′-phosphorylated phosphoinositides has been implicated in a variety of cellular processes, e.g., malignant transformation, growth factor signaling, inflammation, and immunity (Rameh et al (1999) J. Biol Chem, 274:8347-8350). The enzyme responsible for generating these phosphorylated signaling products, phosphatidylinositol 3-kinase (also referred to as PI 3-kinase or PI3K), was originally identified as an activity associated with viral oncoproteins and growth factor receptor tyrosine kinases that phosphorylate phosphatidylinositol (PI) and its phosphorylated derivatives at the 3′-hydroxyl of the inositol ring (Panayotou et al (1992) Trends Cell Biol 2:358-60).
Phosphoinositide 3-kinases (PI3K) are lipid kinases that phosphorylate lipids at the 3-hydroxyl residue of an inositol ring (Whitman et al (1988) Nature, 332:664). The 3-phosphorylated phospholipids (PIP3s) generated by PI3-kinases act as second messengers recruiting kinases with lipid binding domains (including plekstrin homology (PH) regions), such as Akt and phosphoinositide-dependent kinase-1 (PDK1). Binding of Akt to membrane PIP3s causes the translocation of Akt to the plasma membrane, bringing Akt into contact with PDK1, which is responsible for activating Akt. The tumor-suppressor phosphatase, PTEN, dephosphorylates PIP3 and therefore acts as a negative regulator of Akt activation. The PI3-kinases Akt and PDK1 are important in the regulation of many cellular processes including cell cycle regulation, proliferation, survival, apoptosis and motility and are significant components of the molecular mechanisms of diseases such as cancer, diabetes and immune inflammation (Vivanco et al (2002) Nature Rev. Cancer 2:489; Phillips et al (1998) Cancer 83:41).
The main PI3-kinase isoform in cancer is the Class I PI3-kinase, p110α (alpha) (U.S. Pat. No. 5,824,492; U.S. Pat. No. 5,846,824; U.S. Pat. No. 6,274,327). Other isoforms are implicated in cardiovascular and immune-inflammatory disease (Workman P (2004) Biochem Soc Trans 32:393-396; Patel et al (2004) Proceedings of the American Association of Cancer Research (Abstract LB-247) 95th Annual Meeting, March 27-31, Orlando, Fla., USA; Ahmadi K and Waterfield M D (2004) Encyclopedia of Biological Chemistry (Lennarz W J, Lane M D eds) Elsevier/Academic Press). The PI3 kinase/Akt/PTEN pathway is an attractive target for cancer drug development since such modulating or inhibitory agents would be expected to inhibit proliferation, reverse the repression of apoptosis and surmount resistance to cytotoxic agents in cancer cells (Folkes et al (2008) J. Med. Chem. 51:5522-5532; Yaguchi et al (2006) Jour. of the Nat. Cancer Inst. 98(8):545-556).
Malignant gliomas are the most common primary brain tumors in adults. In glioblastoma (GBM), the most aggressive glioma subtype, tumor formation and growth appear to be driven by amplification or overexpression of gene products involved in growth factor-initiated signal transduction acting in cooperation with genetic alterations disrupting cell-cycle control (Holland E C (2001) Nat Rev Genet 2:120-129). Of the genomic alterations described in GBM, PTEN mutation and/or deletion is the most common, with an estimated frequency of 70-90% (Nutt C, Louis D N (2005) Cancer of the Nervous System (McGraw-Hill, New York), 2nd Ed, pp 837-847.). These findings, along with the prognostic value of PTEN status in GBM cases (Phillips H S, et al. (2006) Cancer Cell 9:157-163), suggest the importance of the phosphoinositide 3-kinase (PI3K)/Akt pathway in promoting highly aggressive glial malignancies, as well as the opportunities for treatment with PI3K inhibitors possessing blood-brain barrier penetrant properties.
Malignant gliomas are treated with a combination of surgery, radiation, and temozolomide (TEMODAR™), but these therapies ultimately fail at a high frequency due to tumor recurrence. Additional therapies are needed for delivery of effective concentrations of effective drugs to the brain to treat hyperproliferative disorders, such as glioblastoma and metastatic brain cancer.